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J.F. Sepinsky, S.G. Engle, L.E. DeWarf, E.F. Guinan (Villanova University), I. Ribas (Universidad de Barcelona)
The light variations of the classical T Tauri star (CTTS) SU Aurigae (HD 282624; G2 IIIe; <V> = +9.20 mag; <B-V> = +0.90), like many other CTT stars, are complicated. Long-term photometric observations are made using the 0.8m Automatic Photoelectric Telescope in Arizona. The observations were made from 1993-2001 using Stromgren uvby filters. The light curve varies on time scales of days, months, and years, and displays dramatic, intermittent ``dips'' (\Delta V \approx \Delta y \approx 0.40 mag) that last for several days. Analysis of the small, short period variations in brightness caused by rotational modulation of light by starspots yields a rotational period of about 1.7 days. The starspot/plage sizes have been recently modeled in order to determine the extent of coverage as an estimate of the magnetic field strength or accretion rate in this early-type object. The modeling indicates that spot coverage can be over 1% greater on one side of the stellar surface than on the other, with an average spot hotter than the photosphere by a factor of 10%.
These variations do not appear to be accompanied by significant Stromgren indices changes, which implies possible obscuration of the star by dust with putative properties similar to the ISM. This is most likely due to dust clumps around low mass companions (accreting protoplanets) either warping the circumstellar disk, or exciting tidal waves that heat and puff the disk up locally when dissipating shocks. High dispersion echelle spectra have been obtained with the 4m Blanco telescope at CTIO. One spectrum was secured during a large ``eclipse-like'' event observed during Dec 2000. Current research includes an analysis of these spectra to probe the structure of the accreting gas. We are also conducting a systematic search for regularities in these possible planet-induced obscurations. The discovery of a predictable, periodic event would be the first observation of an eclipse by an accreting protoplanet. This research is supported in part by NSF/RUI Grant AST-00 71260 and the Delaware Space Grant College Consortium through the Undergraduate Summer Research Assistance program.